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A solution has two parts: the solute, which dissolves, and the solvent, which does the dissolving. Together they are the solution. Concentration answers one question — how much solute sits in how much of what?
That last phrase is where marks are lost. Six different formulas exist because six different denominators are useful, and each formula names its own denominator precisely. Mass percentage divides by the solution. Molality divides by the solvent. Molarity divides by the volume of the solution, not the solvent. Mix two of them and you get a number that looks reasonable and is wrong, which is exactly what the distractors are built from.
So learn these formulas as denominator first, numerator second. If you can say what each one divides by, the arithmetic is one line and the trap options stop working. Everything in the next three cards is that one discipline applied six times.
1. 4 g of NaOH (molar mass 40 g/mol) is dissolved in water to make 250 mL of solution. Its molarity is:
2. Which of the following concentration terms does NOT change with a change in temperature?
3. The normality of a 0.5 M solution of H₂SO₄ is:
4. 20 g of glucose (molar mass 180 g/mol) is dissolved in 180 g of water. The molality of the solution is approximately:
5. 100 mL of a 0.5 M NaCl solution is diluted with water to a final volume of 500 mL. The new molarity is:
6. A water sample contains 3 mg of dissolved fluoride per kilogram of water. Its concentration is:
7. 15 g of salt is dissolved in 85 g of water. The mass percentage of the salt in the solution is:
8. A solution contains 2 moles of ethanol and 8 moles of water. The mole fraction of ethanol is: